The flush cycle of most conventional toilets is initiated by moving a lever or chain which pulls a plug or inflated stopper out of its seat in the bottom of a storage tank, releasing the stored water into the bowl and leaving the stopper to float downwardly on the descending water toward its seat. When the water in the bowl reaches a certain threshold level, a siphonic action is created which siphons the water out of the bowl and into a drain pipe which carries the flushed contents to the sewer system. The normal capacity of storage tanks used for this purpose is sufficient to initiate the siphonic action and to refill the trap in the bowl once the flush cycle has begun. The siphonic action continues until the bowl has been emptied and air breaks the siphon, whereupon the trap in the bowl is refilled by the remaining water draining from the tank or, in some models, by the draining water and a supplemental refill passage. As the remaining water drains from the tank into the trap, the stopper or plug floats down to seal the tank and fresh water fills the tank for the succeeding flush cycle.
The timing of this cycle is important both for efficient operation of the toilet and for economy considerations. Proper flushing action and trap refill are needed to remove waste materials and to seal the drain against noxious sewer gases. After the waste materials have been flushed, it is important to seal the tank to prevent water loss as soon as the siphonic action has been interrupted by air and the trap has been refilled. Improper timing of this cycle may result in as much as a gallon or more of water being needlessly wasted, as water added to a full trap, while in sufficient to initiate the siphonic action, will overflow from the overfilled trap to the drain pipe. This waste occurs with every improperly timed flush cycle, resulting in considerable expense both in terms of use of unneeded water and loss of valuable resources. In addition, the wasted water either shortens the period of time a septic tank may be used before it must be emptied, or increases the load placed on the local sewage treatment plant, leading to additional expenses, both individually and collectively.
Since most conventional toilets use approximately five gallons of water per flush, many methods and devices have been developed to reduce this water consumption. These include such simple measures as placing a brick or a weighted plastic bottle in the tank to displace a volume of water; bending the float rod downward to reduce the amount of water required to fill the tank to the operating level; or placing a baffle in the tank against a side wall or around the drain hole to keep some of the water in the tank. More complex measures include using specially designed shallow trap model toilets, or models which use air pressure or mineral oil as a flushing agent. These alternative methods and devices are generally either prohibitively expensive or save water at the expense of flushing performance, disadvantages which are normally unacceptable.